Frequently I see the term “drag freight.” Or drag service or drag era.
It appears that this means a slow freight train. But why would a railroad intentionally run slow trains (if the track can handle fast ones)?
Why would a locomotive be designed “for drag service?”
Does the term refer to placing a priority on length/tonnage of trains, and not worrying about how long the train took to get to its destinations?
Still in training.
Lithonia OperatorDoes the term refer to placing a priority on length/tonnage of trains, and not worrying about how long the train took to get to its destinations?
Even today, there are expedited trains (IM, mostly) and there are manifest trains (as well as unit trains). IM's run about as fast as is allowable (Amtrak notwithstanding). Everything else runs slower.
I could be wrong, and I'm sure someone will come up with the origin of the term.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
tree68I could be wrong, and I'm sure someone will come up with the origin of the term.
No origin, but I always read drag freights having only enough power to maintain a relatively steady and slow speed because the freight being hauled was not time-critical. More power, more speed mean higher costs.
The opposite of Don Prudhomme and Tom McEwan
Drag freight can be any form of freight - the critical element is the train is loaded to the maximum (and some times a little more) tonnage that the locomotives can handle on a given terrirory.
In mountainous territory virtually all trains get loaded and powered to maximum tonnage for 'single' operation (without helpers). A 'drag' over the mountains when it gets to the flatlands will actually become a 'flyer' as it will now have much more power than is necessary to handle the grades that exist on the flatlands.
A 'drag' on the flatlands, will really drag. Back in the 'foggy mists of time' I was tasked with riding a empty auto parts train from New Castle, PA to Akron, OH - relatively speaking 'flatlands'. The power was a single 'brand new' SD-40. The MAXIMUM speed that was managed was 23 MPH (Maximum track speed is 60); when the ground elevates, the load meter Amps go higher and higher and speed goes lower and lower - approaching the minimum continuous speed (the speed at which the heat generated by the traction motor can be sustained indefinately - any slower the increasing traction motor heat will occasion observation of 'short time ratings' - exceed the time of those rating at the expense of a burned up traction motor.)
The ruling grade between New Castle and Willard (Akron is about the midpoint of the run) is Akron Hill - a 1% grade of a little over a mile in each direction as the railroad crosses the Cuyahoga River - with a 15 MPH speed restriction at the bottom of the grade. Minimum continuous speed for a SD-40 is 11 MPH. Long train have the benefit of the rear of the train descending the grade to shove the head end up the grade - short trains will have to handle the entire train being on the ascending side of the hill.
Never too old to have a happy childhood!
Back about 15 years ago, NS had train 177 which ran from Chicago to Ft. Wayne, did some yard work and then went to Chattanooga. It was my favorite train at that time. Why? It had just about everything except intermodal. Typically it was long (well over 100 cars) and heavy.
One day I heard it call signals on the scanner and went down to watch it.
If I recall, it had about 100 loaded grain cars on the front end with an assortment of gons with scrap steel for SDI in Columbia City, In., a few auto racks, boxcars, tank cars, etc.
Total car count was 177 cars (note 177 cars for trains 177) and it crawled thru town at a slow speed.
When you say "drag freight" that 177 comes to mind.
In my mind, a drag needs to have gons with scrap...but that is my definition.
Sadly 177 has been discontinued.
Ed
The drag era really was when you normally had only one engine, a steam engine, to pull a train. The train was built to the capacity of the engine, taking all the tonnage the engine's rating allowed.
They also seemed to switch trains at almost every division point yard. Blocking cars was rare or nonexistant. Cars moved in the general direction of their destination.
You build a train at yard A. Next division point is yard B. The train is built with maximum tonnage, "shorts"- those going to intermediate points between A and B and cars for B, might be first out on the head end. The rest of the train is in whatever order the track standings were for destinations beyond B. The maximum tonnage for an engine, may not reflect the worst grade to be encountered on the district. They may be able to handle 3500 tons out of A, but midway there might be a point where it can only handle 2750 tons. The train may be dispatched with 3500 tons, reduce at a point before the lesser rating begins and continue. If further on the tonnage rating again becomes higher, the train may fill at some point with any available tonnage heading it's way. Tonnage set out waits for available space on a future train heading that way.
Drag freights gradually became unpopular because of the slow handling, not just slow speeds but having to reswitch trains so often, and the cost of switching cars multiple times. Railroads started to block cars in trains for multiple destinations. They started expediting some, but by no means all, freight trains. They were trying to hold onto, or win back, business that they were losing to trucks. Reading old Railroad Magazine/Railroad Stories from the late 1930s, it was a concern back then. Many of the same things discussed now, were discussed then. The biggest difference was then they thought they had a future in many lines (not actual branch lines, etc but categories) of freight. Some of which has either been lost by the railroads or no longer wanted.
Jeff
My recollection of a drag is one that stopped at every station where there was local switching to be done. This was much more common in the mid 1900's with the sixteen hour on duty law. Now we have 'locals' when there is a need for this.
Ed:
In the PSR world we now inhabit; I believe drag freights like your old 177 are being reborn.
I watched a southbound CSX freight crawl through Dalton, GA last evening with one motor as leader and a second single motor as mid train DP. No idea what car count or trailing tonnage was but, it took the entire train better than eight minutes to pass and I doubt he was moving much faster than 20-25 MPH.
Back about 15 years ago, NS had train 177 which ran from Chicago to Ft. Wayne, did some yard work and then went to Chattanooga. It was my favorite train at that time. Why? It had just about everything except intermodal. Typically it was long (well over 100 cars) and heavy. One day I heard it call signals on the scanner and went down to watch it. If I recall, it had about 100 loaded grain cars on the front end with an assortment of gons with scrap steel for SDI in Columbia City, In., a few auto racks, boxcars, tank cars, etc. Total car count was 177 cars (note 177 cars for trains 177) and it crawled thru town at a slow speed. When you say "drag freight" that 177 comes to mind. In my mind, a drag needs to have gons with scrap...but that is my definition. Sadly 177 has been discontinued. Ed
Juniata ManEd: In the PSR world we now inhabit; I believe drag freights like your old 177 are being reborn. I watched a southbound CSX freight crawl through Dalton, GA last evening with one motor as leader and a second single motor as mid train DP. No idea what car count or trailing tonnage was but, it took the entire train better than eight minutes to pass and I doubt he was moving much faster than 20-25 MPH. Back about 15 years ago, NS had train 177 which ran from Chicago to Ft. Wayne, did some yard work and then went to Chattanooga. It was my favorite train at that time. Why? It had just about everything except intermodal. Typically it was long (well over 100 cars) and heavy. One day I heard it call signals on the scanner and went down to watch it. If I recall, it had about 100 loaded grain cars on the front end with an assortment of gons with scrap steel for SDI in Columbia City, In., a few auto racks, boxcars, tank cars, etc. Total car count was 177 cars (note 177 cars for trains 177) and it crawled thru town at a slow speed. When you say "drag freight" that 177 comes to mind. In my mind, a drag needs to have gons with scrap...but that is my definition. Sadly 177 has been discontinued. Ed
CSX has been a Drag Freight railroad for at least 30 years. The only trains that had more power than was required for maximum tonnage were intermodals - they would have nominally 1 more unit than maximum tonnage per unit would allow.
A second aspect of assigning power to a specific merchandise or intermodal train is always what will be the power requirements at the other end of the line to handle trains in the return direction. Daily volumes vary on scheduled trains - sometimes you end up with a train that actually has more power than drag tonnage would indicate.
Thanks for the explanations, guys.
The term "drag freight" brings to mind the similar "hold for tonnage", meaning a train's departure was to be delayed until maximum tonnage had been accumulated. Immediately after the NYC/PRR merger, "held for tonnage" was enough to send Al Perlman ballistic and could get you fired. He insisted that, if a train was scheduled to depart at 7:00, the dust was settling behind the markers at 7:01.
ChuckAllen, TX
To my knowledge the "drag freight" era was the period from roughly 1910-1935. Before that, engines were relatively small, like 2-8-0s for freight trains. Freight trains then were relatively short, unless you had double-(or triple-)headers.
When Mallet / Articulated engines came into use, railroads could run much longer trains using one big engine instead of running a long train with multiple smaller engines (thereby not having to pay multiple crews). Early Mallets had very small drivers, since that allowed them to start and pull long, heavy trains without slipping. This, however, limited their top speed - a USRA 2-6-6-2 would be limited to running at 20 MPH or less for example. Running faster was difficult in part because it was hard to counterbalance small drivers properly.
So you ended up with very long trains being pulled by very large steam engines, trundling along at 12-15 MPH. That would be a "drag freight".
When 'superpower' engines started to be built in the late twenties, railroads found they could have engines with larger drivers like 2-8-4s or 4-8-4s that could pull as long a train as a drag freight engine, but at a much faster speed.
My grandfather was a 30+ year engineer/fireman on the VGN. He told me the term was from: dragging coal out of the hollers in WV.
Some railroads and engine types come to mind that operated beyond the time period you suggest: 2-10-0s on the PRR, 2-10-2s on many lines.
How long the drag era lasted also depended on what was being "drug". Manifests normally picked up speed many years before mineral trains did.
A drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there".
So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight.
Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s.
Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton.
However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) .
Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
oltmanndA drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there". So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight. Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s. Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton. However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) . Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish.
CSX does NOT dispatch trains based on axles - they dispatch trains based on tonnage ratings - the tonnage ratings define the limits of drag tonnage on a territory. Tonnage ratings do not take into consideration helper districts. A HP/ton figure is included on CSX Train Documents, however, it is there for information only.
Where there are helper districts, trains are powered for for the adjoining less graded territories with the helpers supplying the necessary power to defeat the mountain grade.
The only trains CSX supplies 'extra' power to are intermodals. With the implementation of PSR and DPU on the intermodal trains - they are being dispatched at drag ratings for the power - longer trains with in train DPU's but drag tonnage ratings for the train as a whole.
oltmannd A drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there". So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight. Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s. Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton. However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) . Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish.
UP switched from hp/ton to Tons per (equvilant) Powered Axle. That doesn't mean everything gets the same TPA requirement. Just as not every train had the same hp/ton requirement. Intermodals may have a 250 TPA while a coal train may have a 800 TPA over the same crew district. The lower the TPA, the faster a train should be able to go. Most of our coal trains have a 575 TPA on my district. Some, where they want to save fuel and lug around a isolated/dead engine on a train, get the 800 TPA.
jeffhergert oltmannd A drag freight is one that is powered to ascend the ruling grade on it's route at the locomotive consist's minimum continuous speed. It is powered to "get there" and not stall. A scheduled freight, in comparison, is powered according to a HP/ton ratio and is supposed to "get there on time", not just "get there". So, if you had a RR with a 1.0% ruling grade, and you needed 1.20 HP/ton to maintain your schedule, lets look at how you might power a drag freight vs a scheduled freight. Let's say you have a 7500 ton train. You need about 150,000# TE to get over the hill without stalling. That's right about what a pair of SD40s can do. But, that leaves the train with 0.8 HP per ton. To make schedule, you'd need 9000 HP, or three SD40s. Railroads that power trains by "axles" are really running their whole railroad at drag ratings. Depending on the locomotives you buy and employ, the HP/ton is kind of baked in and schedules are somewhat supported by HP/ton. However, as the railroads have gone to AC locomotives, the HP that comes along with each lb of TE is less. If they continue to dispatch trains on "axles" the result will be slower train speeds (and some fuel savings!) . Which is the "best" was to go about powering trains depends entirely on what it is you're trying to accomplish. UP switched from hp/ton to Tons per (equvilant) Powered Axle. That doesn't mean everything gets the same TPA requirement. Just as not every train had the same hp/ton requirement. Intermodals may have a 250 TPA while a coal train may have a 800 TPA over the same crew district. The lower the TPA, the faster a train should be able to go. Most of our coal trains have a 575 TPA on my district. Some, where they want to save fuel and lug around a isolated/dead engine on a train, get the 800 TPA. Jeff
That's very different from NS. I didn't know! Thanks for explaining.
Going with TPA and varying it by train type on a route is kind of a backhanded way for getting to HP/ton - provided it's based on the locomotive with the lowest HP per (equivalent) axle.
DR DENNIS GORDANI am late to the discussion, but note that all comments relate to diesel electrics, while "drag freight" started in the steam era, when there was no issue with overheating at low speed, so slogging along with the least power that kept things rolling was safe and economical.
The reality is the Diesel-Electrics of generations upto the start of AC traction in the mid 1990's, had 'short time ratings' developed from the maximum amperage the traction motors could handle without 'melting down' from the excessive heat generated in the motor windings. The short time ratings come into play when the train is moving too slowly - as train speed increases amperage the traction motors require decreases.
Steam engines in 'drag' service, generally had small driving wheel diameters, faster steam engines had larger driving wheel diameters. The reality is that steam engines at maximum load in drag serice would maintain 5 MPH. The MCS of diesel-electrics in freight service range from 9 to 12 MPH and thus diesel-electrics 'could' haul the same amount of freight as a steam engine at roughly twice the speed and not have to stop for water during the trip.
BaltACD 'melting down' from the excessive heat generated in the motor windings.
I always liked the term "bird's nested" for overheated motors. I can picture in my mind what the windings look like.
_____________
"A stranger's just a friend you ain't met yet." --- Dave Gardner
Paul of CovingtonI always liked the term "bird's nested" for overheated motors.
Overheating melts the insulation between windings, and likely produces a ground-fault or short long before the copper actually starts expanding enough to foul the stator poles.
When I was little I always thought about open spinning reels and how not to use them when I read about birdsnesting.
Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done ) can cause 'stall burns' inside DC motors.
AC motors seem relatively immune to this type of damage, as long as the traction motor blowers are working properly. I recently saw a newer GE unit with a failed TM blower still working away, it was giving off a very noticeable smell of hot grease and metal.
Greetings from Alberta
-an Articulate Malcontent
SD70Dude Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done )
Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done )
Commenting for a friend, are you?
Lithonia Operator SD70Dude Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done ) Commenting for a friend, are you?
It works very well in certain situations, or so I've been told.
cefinkjr The term "drag freight" brings to mind the similar "hold for tonnage", meaning a train's departure was to be delayed until maximum tonnage had been accumulated. Immediately after the NYC/PRR merger, "held for tonnage" was enough to send Al Perlman ballistic and could get you fired. He insisted that, if a train was scheduled to depart at 7:00, the dust was settling behind the markers at 7:01.
Hmmm.. Hold for tonnage.. Geez thats sounds eerily similar to... Oh nevermind...
SD70Dude Trying and failing to start a heavy train or holding a train still with the throttle (which no one has ever done ) can cause 'stall burns' inside DC motors.
Stall burns presumably being a burned out winding on the armature. When the motor is turning, any given winding is only conducting current for a relatively small fraction of the time and this has a chance to cool down before conducting current again. My understanding is that DC locomotives often have a minimum continuous speed to prevent stall burns.
AC induction motor windings have varying current even when the rotor is not turning in conjunction with beefier windings help prevent stall burns.
Erik_MagAC induction motor windings have varying current even when the rotor is not turning in conjunction with beefier windings help prevent stall burns.
I would have said this also applies to operations over the road, but that story about the GE making traction power with the TM blower disabled, and the hot-metal-and-grease smell, has made me profoundly nervous. I can see providing military equipment with the "RUN NOW -- no backchat" option, but not locomotives. On the other hand, in this era of PSR I can almost see the attractiveness of a Northstar-style limp-home power capability...
I could argue that the stator windings on an AC motor are equivalent to the field windings on the DC motor. In both cases, the duty cycle doesn't change...
The major difference is in the armature, where the windings of an induction motor are substantial copper bars that don't need insulation. Another difference is a much larger fraction of the bars are conducting current on the induction motor as opposed to the fraction of active windings in a DC motor. Finally, in a stalled induction motor, the field still needs to be rotating in order to induce the torque producing currents in the copper bars composing the "squirrel cage", and thus spreading out the heat.
As for number of windings on a DC motor: IIRC, modern traction motors can have up to 1500V applied to the terminals. DC machine practice is to limit potential difference between commutator bars to 20V, so we're looking at 75 bars (or more) between the positive and negative brushes. Each pair of bars corresponds to one winding, so under normal operation, each winding has a duty cycle of a few per cent. Running full current through a winding at 100% duty cycle is going to create some serious temperature rise.
Bottom line is that the switch to AC motors was done for good reason.
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